The present invention relates generally to the field of circuit breakers and more specifically to a circuit breaker having a programmable amplifier.
A circuit breaker is typically characterized by a current rating which conventionally corresponds to the current at or above which the circuit breaker will trip (open), disconnecting a source of power from a load. The circuit breaker includes a current transformer (CT) having a winding in close proximity to a power line carrying alternating current. The current transformer provides a sense signal (e.g., a secondary current signal induced by the alternating current of the power line) representative of the power signal in the power line to the control circuitry of the circuit breaker. The control circuitry monitors the secondary current signal and trips the unit based on the monitored signal.
Circuit breakers come in a wide range of current ratings (e.g., 63 Amp, 200 Amp, 250 amp, 1600 Amp, etc.). Typically, each circuit breaker has a different CT having a rating corresponding to the desired rating of the circuit breaker. The winding of the CT is manufactured to be particularly suitable with the desired rating of the circuit breaker and correspondingly suitable to the current load carried in the power line. With the advent of electronic trip units (ETUs), for monitoring the secondary current signal and for tripping the circuit breaker, it has become necessary to manufacture an ETU for each line of circuit breakers based on the nominal circuit breaker rating.
According to one system, the ETU is provided with a hard-coded program that tells the ETU it is, for example, a 200 Amp circuit breaker. The drawback of this system is that ETUs must be inventoried for each current rating which adds significant cost and complexity to the manufacturing process of the circuit breakers. Another system utilizes programmable ETUs with software tables for all ratings of circuit breakers. A plastic connector (e.g., a jumper) is provided on the circuit board which couples one of a plurality of pins to ground to indicate to the ETU its rating and, correspondingly, which software table to use to interpret (e.g., scale) the secondary current signal. This system requires additional memory space, circuit board space, and added installation steps (e.g., to properly connect the jumper) which adds cost and complexity to the design.
There is a need for an improved circuit breaker design that does not require the inventory or cost associated with manufacturing and installing customized ETUs for a large number of circuit breakers and which does not result in large amounts of unused memory, circuit board space or added installation costs. There is also a need for an improved circuit breaker design that would provide for a CT having one rating to be used in circuit breakers having a range of ratings to reduce the costs associated with manufacturing and inventorying a wide array of CTs. Further, there is a need for an improved circuit breaker design that would allow the same microprocessor and software program to be used for current transformers rated from 63 Amps to 1600 Amps, and beyond. Further still, there is a need for an improved circuit breaker design that would facilitate ease of maintenance, repair, and installation of the circuit breaker.
One embodiment of the invention relates to a circuit breaker having a power line for carrying a power signal from a source to a load and a current transformer configured to sense the power signal and provide a sense signal based on the power signal at a first terminal. The circuit breaker includes a control circuit configured to receive a first data message and to provide a second data message based on the first data message at a second terminal. The control circuit further includes a programmable amplifier coupled to the first terminal and the second terminal configured to receive the sense signal, to receive the second data message, to amplify the sense signal representative of the second data message, and to provide the amplified sense signal at a third terminal.
Another embodiment of the invention relates to a method for constructing a circuit breaker, including: providing a circuit breaker component having a computer-readable indicia representative of a desired rating of the circuit breaker; coupling an electronic module to the circuit breaker component, the electronic module including: a control circuit configured to receive a first data message and to provide a second data message based on the first data message at a first terminal; and a programmable amplifier coupleable to a current transformer and the output terminal configured to receive a sense signal from the current transformer, to receive the second data message, to amplify the sense signal based on the second data message, and to provide the amplified sense signal at a second terminal. The method further includes scanning the computer-readable indicia and providing the first data message to the control circuit, wherein the first data message is based on the scanned computer-readable indicia.
Yet another embodiment of the invention relates to a method for repairing a circuit breaker, including removing a first electronic trip unit from the circuit breaker; coupling a second electronic trip unit to the circuit breaker, the second electronic trip unit including: a control circuit configured to receive a first data message and to provide a second data message based on the first data message at a first terminal and a programmable amplifier coupleable to a current transformer and the output terminal configured to receive a sense signal from the current transformer, to receive the second data message, to amplify the sense signal based on the second data message, and to provide the amplified sense signal at a second terminal. The method further includes providing the first data message to the control circuit, whereby the second electronic trip unit is programmed with the first data message.
Still another embodiment of the present invention relates to a circuit breaker, having: means for sensing a power signal and for generating a sense signal representative of the power signal; means for amplifying the sense signal based on a data message; means for providing the data message to the means for amplifying; and means for tripping the circuit breaker based on the amplified sense signal.